The normal structure of the tooth anatomy involves both the tooth itself, as well as the bone that it connects to. The tooth socket is called the alveolus, and the bone that surrounds the socket is the alveolar bone. The tooth and alveolus are connected to each other by the periodontal ligament. This ligament is made of connective tissue and acts as a “shock absorber” to help protect the tooth and the jaw from damage. This ligament allows for a very small amount of movement of the tooth in the socket, yet holds the tooth in place.
The tooth itself consists of 3 parts: enamel, dentin, and pulp. The enamel is the tough non-porous outer coating of the tooth that is normally the only part of the tooth that can be seen. The dentin is a more porous bony material that lies beneath the enamel, and is softer than enamel. The dentin has microscopic tubules present, which normally allow nutrients to diffuse from the pulp into the dentin, to keep the tooth structures alive and healthy. The pulp consists of the blood vessels and nerves that supply both nutrients and sensation to the tooth.
When a tooth has an impact, thermal (heat) damage, or long-term improper pressure (usually from teeth that do not fit together properly), it can cause direct inflammation of the pulp (pulpitis) or disruption of the blood supply to the tooth. Either of these will result in swelling of the pulp, bleeding, and blood leakage into the dentinal tubules. This causes discoloration of a tooth from pink to purple. If this is a long-standing problem, the tooth will often take on either a gray or an ivory discoloration. The affected tooth or teeth are, in almost all cases, no longer living teeth.
When a tooth is no longer living (also referred to as non-vital), the pulp of the tooth becomes necrotic (a term used to described dead tissue that is starting to decay). This results in chronic pain, leakage of the necrotic material into the blood stream, and makes the tooth a place that can harbor bacteria from the bloodstream, resulting in the development of a tooth abscess.
In the past, we would determine if a tooth has become non-vital is by taking dental x-rays to evaluate the affected tooth. There are certain changes in the appearance of a tooth that confirm it is a non-living tooth. However, a recent unpublished study showed that with discolored teeth, only about 40% of the teeth had changes in their appearance on x-rays, but 97% of the teeth were, in fact, non-vital.
If a tooth is discolored, in most cases it is safe to assume that the tooth is non-vital (not living). For a non-vital tooth, there are only 2 options. We must either do root canal therapy or extract the tooth.
When we do root canal therapy on a discolored tooth, we make an opening in the enamel to allow access to the inside of the tooth. Then, we remove the dead material from inside the tooth and fill the pulp chamber with an inert material. Then we do a composite restoration, or “filling” in the tooth.
The advantage of root canal therapy is that we keep this tooth as a functional tooth in the mouth. The disadvantages are the following: there is increased cost of a root canal over extraction, follow-up x-rays are required at a later date, and that there is a very small chance of failure of the procedure. After root canal therapy, dental x-rays are taken 9-12 months later, to make sure the procedure was successful. In animals dental x-rays can only be taken with the animal under anesthesia. If a root canal fails, then the options that we have are to either do a less involved surgical procedure called an apicoectomy (this is not always an option, depending upon the tooth that is affected), in order to save the tooth, or extract the tooth at that time.
As for extraction, the advantages are that it is a relatively simple procedure with minimal follow-up, minimal chance of significant complications, and that it is less expensive than root canal therapy. The disadvantage is that the pet loses the function of the affected tooth.
In some cases, especially if the affected tooth has an abscess at the time of evaluation or has other complicating factors (such as periodontal disease), then root canal therapy is not an option, due to the long term increased chance of failure of the procedure, and extraction becomes the only reasonable option.
Exact estimate for the cost of root canal therapy and follow-up x-rays versus extraction will vary depending upon the specific tooth that is affected, as well as other circumstances surrounding the procedure. Estimates are given on a case-by-case basis.